Sealed-type remote pressure-monitoring device and method for fabricating the same

ABSTRACT

Disclosed are a remote pressure-monitoring device and a preparing method thereof. The device comprises a metal electrode on a glass substrate, a capacitive sensor made of a silicon diaphragm, and an electroplated inductor electrically connected, in parallel, with the sensor. The glass substrate and the silicon are electrically bonded to form an LC resonator. For the fabrication of the device, first, a metal electrode which plays a role as a lower electrode for a capacitive pressure sensor is deposited on the glass substrate with the same coefficient of thermal expansion as that of silicon. An inductor is formed at a thickness by copper electroplating, surrounding the metal electrode at a predetermined distance. A silicon substrate is anisotropically etched to form a space for enveloping the metal electrode at a central area and to form a groove around the space. Boron ions are diffused lightly into the space and deeply into the groove to form etch barriers thereat, followed by bonding the silicon substrate on the glass substrate through an electrical contact in such a way that the metal electrode and the inductor are enveloped in the space and the groove, respectively. Then, the silicon substrate is etched out from its rear side to the extent that the etch barriers are exposed.

BACKGROUND OF THE INVENTION

1. 1. Field of the Invention

2. The present invention relates to a sealed-type remotepressure-monitoring device. More particularly, the present inventionrelates to a sealed-type remote device for monitoring the internalpressures of animal organs, especially, the human eyeballs, heart, brainand so on. Also, the present invention is concerned with a method forfabricating such a device.

3. 2. Description of the Prior Art

4. Medicinally, the internal pressures of human organs havesignificantly important meanings in treating the organs. Particularly,measuring the internal pressure of the eyeball, that is, intraocularpressure is very important because higher intraocular pressures thannormal may damage visual cells. Once being damaged, the visual cells arevirtually impossible to recover to a normal state. In the worst case, ifnot suitably treated in time, the patients may lose their sightpermanently.

5. For this reason, extensive research has been made on methods formeasuring intraocular pressures, for several decades. The intraocularpressure-sensing methods developed thus far are generally divided into aphysically sensing method, an optically sensing method, and a directlysensing method using a sensor.

6. The physically sensing method is characterized in applying physicalforce to the eyeball to sense the intraocular pressure. For example, analready known pressure is applied to the eyes, followed by measuring theflexure of the eyeball. Another example of this physically sensingmethod is to drop glass beads or metal beads on the eyeball and then tomeasure the height to which they bounce.

7. As for the optically sensing method, it takes advantage of the changein the optical refractive index or reflection of the eyeball. Forexample, after a medium such as air is injected to the eyes, an opticalchange in the eyeball is measured. Alternatively, a reflection change inthe eyeball may be detected by applying a pressure to the eyeball.

8. The directly sensing method utilizes a sensor in measuringintraocular pressures. This method has an advantage over theabove-mentioned indirect methods in that more accurate values for theintraocular pressure of the eyeball can be obtained by virtue of thesensor which is directly inserted in the eyes. In this regard, thepressure sensor inserted in the eyes transmits the information on theinternal pressure of the eyeball to the outside by use of inductivecoupling using an inductor.

9. Of the three representative intraocular pressure-sensing techniques,the directly sensing method has become predominant in recent years forits accuracy and convenience. In the physically or optically sensingmethod, a stimulus must be given to the eyeball whenever a measurementis taken on the intraocular pressure, imposing a significant burden onthe patients who should be continually observed. What is worse, theseindirect methods are inaccurate in sensing the internal pressures. Fromthe late 1960s, many attempts have been made to measure intraocularpressures with the aid of wireless devices with advances in thesemiconductor industry.

10. A remote sensing technique related to the invention is found in thearticle “Miniature Passive Pressure Transensor for Implantation in theEye”, IEEE Trans. BME. 14, pp. 74-83, 1967, yielded to C. C. Collins,which discloses a pressure-sensing device having two coiled inductorswhich are faced toward each other with a connection and sealed in aplastic package. In this structure, the plastic package is bent uponpressure application so that the distance between the two inductorsvaries. In turn, the mutual inductance and spray capacitance between thetwo coils also varies according to the change of the distance, givingrise to a change in the resonant frequency. Thus, by measuring thisresonant frequency, the intraocular pressure can be monitored.

11. Another prior technique is exemplified by the article of L.Rogengren, entitled “A System for Passive Implantable Pressure Sensors”,in Sensors and Actuators, A43, pp. 55-58, 1995. In the system, aninductor is wound around a pressure sensor made of two micromachinedsilicon substrates which are bonded and connected to each other in ahybrid manner. With a connection to an electrode drawn from thesubstrates, the inductor is enveloped in a resin. When pressure isapplied to the system, the capacitance of the pressure sensor ischanged, so that a corresponding change is brought about in theresonance frequency of the device because of the inductor coupled inparallel. Hence, the pressure applied can be evaluated by measuring thechanged resonance frequency.

12. The conventional methods above mentioned, however, suffer fromsignificant disadvantages. For instance, since the pressure-sensingdevice suggested in the article of C. C. Collins exposes important partsof the device externally, a plastic case harmless to the body is neededfor envelopment. The system disclosed in the L. Rogengren's article isdisadvantageous in that, because the pressure sensor is made of twosilicon substrates, the Q value is lowered owing to the parasitecapacitance between the two silicon substrates and to the hybridcoupling manner. In addition, another disadvantage of this system isthat a resin is used to seal the outer inductor, requiring a harmlessplastic envelope for the system.

13. In many patents are found the prior arts related to the presentinvention.

14. U.S. Pat. No. 4,922,913 discloses an intraocular pressure sensorwhich uses a piezo resistive pressure sensor. This sensor suffers from afatal disadvantage in that, to measure the intraocular pressure of theeyeball, the sensor in the eyeball must be connected to an externaldetecting device via a wire. Owing to the wire drawn from the eye, it ishighly apt to be infected with bacteria and the humors in the eyeballmay flow out.

15. Another pressure-sensing technique is disclosed in U.S. Pat. No.4,089,329, entitled “noninvasive continuous intraocular pressuremonitor”. According to this invention, a change in intraocular pressureinduces a motion of a strain gauge, owing to which a resistance changeis caused. This resistance change is detected by a transmitter, therebytransmitting the intraocular information to the detection device withoutthe use of wires. However, since the pressure sensor is separated fromthe transmitter, the humors in the eyeball may flow out.

16. U.S. Pat. No. 5,005,577, entitled “Intraocular lens pressuremonitoring device”, is similar to the C. C. Collins' article in asensing manner, disclosing that two coiled inductors are faced towardeach other with a connection and a change is brought about in thedistance therebetween in dependence on pressure, allowing the spraycapacitance and mutual inductance between the coils to vary. Theresonance frequency thus changed is detected to monitor the changedpressure. This device, however, has a disadvantage of being enveloped ina cumbersome plastic case. The plastic case itself is not harmful to thebody.

SUMMARY OF THE INVENTION

17. Therefore, it is an object of the present invention to overcome theabove problems and to provide a sealed-type remote pressure-monitoringdevice, which directly allows the detection of the internal pressure ofanimal organs without the use of wires.

18. It is another object of the present invention to provide asealed-type remote pressure-monitoring device, which itself can beinserted into the body without being packed in harmless plastic.

19. It is a further object of the present invention to provide asealed-type remote pressure-monitoring device, by which the internalpressure of animal organs can be measured with high accuracy.

20. It is still a further object of the present invention to provide asealed-type remote pressure-monitoring device, which has few parasiticcomponents in the pressure sensor and a reduced resistance in aninductor so as to obtain a high Q value.

21. It is still another object of the present invention to provide amethod for fabricating such a sealed-type remote pressure-monitoringdevice.

22. Viewed from a first aspect, the present invention provides a devicefor remote monitoring the internal pressure of animal organs, saiddevice comprising: a glass substrate having a coefficient of thermalexpansion as large as that of silicon; a metal electrode which is formedat a predetermined thickness on a central area of the glass substrate;an inductor which is formed at a predetermined thickness on the glasssubstrate by a copper electroplating process, surrounding the metalelectrode at a predetermined distance; a silicon cover, consisting of asilicon diaphragm and a cover structure, which is bonded on the glasssubstrate in such a manner that the silicon diaphragm and the coverstructure cover the metal electrode and the inductor, respectively,without a direct contact between them, thereby shielding the metalelectrode and the inductor from the external environment; a contactwhich is formed on the glass substrate, extending from a junctionbetween the glass substrate and the silicon cover to the inductor toelectrically connect the silicon cover to the inductor.

23. Viewed from a second aspect, the present invention provides a methodfor fabricating a sealed-type device which remotely senses the internalpressure of animal organs, said method comprising the step of:depositing a metal electrode on a central area of a glass substrate witha coefficient of thermal expansion as large as that of silicon, themetal electrode playing a role as a lower electrode for a capacitivepressure sensor; forming a pattern of an inductor at a predeterminedthickness by copper electroplating, said inductor surrounding the metalelectrode at a predetermined distance; etching a central area of asilicon substrate to form a space for enveloping the metal electrode;forming a pattern of a groove around the space in the silicon substrateby a etching process; diffusing boron ions shallowly into the space anddeeply into the groove to form etch barriers thereat; bonding thesilicon substrate on the glass substrate through an electrical contactin such a way that the metal electrode and the inductor are enveloped inthe space and the groove, respectively; and etching the siliconsubstrate from its rear side to the extent that the etch barriers areexposed.

BRIEF DESCRIPTION OF THE DRAWINGS

24. The above and other objectives and aspects of the invention willbecome apparent from the following description of embodiments withreference to the accompanying drawings in which:

25.FIG. 1 is a cross sectional view of a remote pressure-monitoringdevice according to the present invention;

26.FIG. 2 is a partially broken perspective view of the remotepressure-monitoring device shown in FIG. 1;

27.FIG. 3 is an illustration for explaining an electrical contactbetween an inductor and a capacitive pressure sensor in the remotepressure-monitoring device according to the present invention;

28.FIG. 4 is a schematic plan view of the remote pressure-monitoringdevice viewed from the view point of a glass substrate;

29.FIGS. 5a to 5 c are cross sectional views taken along lines shown inFig. 4;

30.FIG. 6 is an illustration for explaining the process for fabricatingthe remote pressure-monitoring device according to the presentinvention;

31.FIG. 7 is an electron micrography showing a portion of the remotepressure-monitoring device, in which the silicon substrate is etched atthicknesses of 3 μm and 50 μm to form a space for a capacitor electrodeand a groove for the inductor;

32.FIG. 8 is an optical micrograph showing a pattern of a photoresistfilm 30 μm thick;

33.FIG. 9 is an electron micrograph showing inductor coils 30 μm thickformed by copper electroplating; and

34.FIG. 10 is a schematic diagram illustrating a remotepressure-monitoring procedure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

35. The application of the preferred embodiments of the presentinvention is best understood with reference to the accompanyingdrawings, wherein like reference numerals are used for like andcorresponding parts, respectively.

36. In the present invention, a glass substrate and a silicon substrate,both harmless to the human body, are used as base materials infabricating an intraocular pressure sensor, so that no additionalpackages are needed for the sake of securing safety. While the glasssubstrate is provided to integrate a sensor and a transmitter thereonaccording to a semiconductor process, it is electrically combined withthe silicon substrate in such a manner that the sensor and transmitterare sealed. In detail, when the silicon substrate and the glasssubstrate are put together, the resulting united module comes to have astructure in which the pressure sensor and an inductor are concealed.Therefore, not only the capacitive pressure sensor, but also theinductor is sealed per se, so no packages are needed.

37. Since Au deposited on the glass substrate and boron-diffused silicondiaphragm are used as a lower electrode and an upper electrode of thecapacitive pressure sensor, the device of the present invention has farfewer parasitic components than have the conventional pressure sensorswhich are made of two laminated silicons. Also, the present invention ischaracterized in that all of the parts of the device, except for thesilicon diaphragm and the glass substrate, both harmless to the humanbody, are per se sealed by integrating the inductor and the capacitancein the chip. Therefore, the device itself can be inserted into the bodywithout being packed in, for example, harmless plastic.

38. With reference to FIGS. 1 to 5, there is illustrated an LC-resonantpressure-monitoring device according to the present invention.

39.FIG. 1 shows the structure of the LC-resonant pressure monitoringdevice in a cross sectional view while FIG. 2 is a partially brokenperspective view of the device. As shown in these figures, the devicecomprises a glass substrate 20 with a metal electrode 210 formed at apredetermined thickness on a central area of the glass substrate, aninductor 80 formed at a predetermined thickness on the glass substrate20, surrounding the metal electrode 210 at a predetermined distance, anda silicon cover 50 consisting of a silicon diaphragm 60 and a coverstructure 40, bonded on the glass substrate 20, said diaphragm 60covering the metal electrode 210, said cover structure 40 accommodatingthe inductor 80. Thus, the silicon cover plays a role in shielding themetal electrode and the inductor from the external environment. On theglass substrate 20 is formed a contact through which the silicon cover50 is electrically connected to the inductor 80. The glass substrate 20is made of Corning 7740 with a coefficient of thermal expansion as largeas that of the silicon substrate 10, so the thermal stress generatedowing to the difference in the coefficient of thermal expansion whenbonding the silicon substrate 10 on the glass substrate 20 can beminimized.

40. A method for fabricating the device is described in FIGS. 5a to 5 cand FIG. 6.

41. The fabrication of the remote intraocular pressure-measuring deviceis conducted in two processes: a silicon substrate process and a glasssubstrate process. The silicon substrate and the glass substrate whichare obtained by conducting the two processes, respectively, are combinedby anode bonding.

42. First, the glass substrate process is sub-divided into a metaldepositing step and a copper plating step by which the lower electrode210 of the capacitive pressure sensor and the inductor 80 are formed,respectively. The planar glass substrate 20 is etched to a depth of 200nm at its central region, followed by depositing Au/Cr in a thickness of220 to 230 nm on the etched central region to form a metal electrode 70.As a result, this metal electrode 70 becomes higher than the glasssubstrate 20 by approximately 20 to 30 nm. The reason why the metalelectrode 70 is made at such a height is that, when the siliconsubstrate 10 obtained by the silicon process is electrically bonded onthe glass substrate 20, the silicon substrate 10 and the inductor 80 areeach optimally brought into an electrical contact, as denoted thereference numerals 330 and 340 in FIG. 3, with an electrical junctionbetween the capacitive sensor and the inductor 80.

43. For the formation of the inductor 80, copper electroplating isuseful. Preferably, the copper used in the present invention has anelectric conductivity (ρ) as high as about 1.7 μΩ. In order for theinductor 80 to have a high Q value, it must be of small resistance andlarge inductance. Plating the copper at a large thickness can reduce theresistance while narrowing the space between inductor lines can increasethe inductance. Accordingly, a photoresist film 100 is patterned at ahigh aspect ratio. In the present invention, copper is electroplated ata thickness of 30 μm and used to obtain a photoresist 100 in which theratio of line to space is 15 μm/15 μm.

44. The process which is performed on the silicon substrate comprisesetching and diffusing.

45. First, as for the etching, it is conducted to form a space 30 forseparating the silicon substrate 10 from the metal electrode 70 formedon the glass substrate 20 and to form a groove 40 for accommodating andprotecting the inductor 80. To this end, the silicon substrate 10 isanisotropically etched using KOH. Following this, boron is diffused onthe etched areas, that is, the space 30 for the capacitive sensor andthe groove 40 for the inductor, to form etch-preventive films 50 and 60,as illustrated in FIG. 6.

46. Next, the resulting silicon substrate 10 is aligned with the glasssubstrate 20 in such a way that the space 30 and the groove 40correspond to the metal electrode 70 and the inductor 80, respectively.Subsequently, the silicon substrate 10 and the glass substrate 20 aresubjected to an electrical bonding process at 400° C. and 800 V.

47. Thus, the inductor 80 is electrically connected to the capacitanceand finally, the silicon 10 is electrically bonded on the glasssubstrate 20. Thereafter, the silicon substrate 10 is etched out fromits rear until the etch-preventive film remains alone.

48. During the fabrication of the sealed-type remote pressure-monitoringdevice according to the above procedure, important parts had theirmicrophotographs taken, as shown in FIGS. 7 to 9.

49. In the electron micrograph of FIG. 7, there are shown the space 30for the capacitor electrode and the groove 40 for the inductor, whichare etched to a depth of 3 μm and 50 μm, respectively. FIG. 8 shows apatten of the photoresist film 100 which is 30 μm thick, in an opticalmicrograph. The inductor coils 80 which are formed at a thickness of 30μm by a copper electroplating process are shown in the electronmicrograph of FIG. 9.

50. The pressure-monitoring device of the present invention, asillustrated above, has a structure in which the inductor is in parallelconnected to a variable capacitive pressure sensor. Varying withpressure, the capacitive pressure sensor consists of a P⁻-diffusedsilicon film 60 and the metal electrode 210 deposited on the glasssubstrate 20. When being applied with pressure, the silicon diaphragm iswarped to alter the capacitance of the capacitive pressure sensor. Thepressure-monitoring device according to the present invention isdesigned to have its resonant frequency vary in dependence on thecapacitance. Therefore, a change in the resonant frequency indicates achange in the pressure, enabling evaluation of the internal pressure.

51. With reference to FIG. 10, the principle under which thepressure-monitoring device of the present invention is operated isillustrated. If an external saw tooth wave drives a VCO, the voltageacross the opposite ends of a driving coil suddenly changes when beingmeasured around the resonance frequency of the pressure-monitoringdevice. This change of the voltage is attributed to the fact that the LCresonance causes the output impedance from the driving coil to suddenlyvary around the resonance frequency of the pressure device. At thistime, this variation allows the resonance frequency of thepressure-monitoring device to be calculated, thereby measuring thepressure applied to the pressure-monitoring device.

52. As described hereinbefore, the remote pressure-monitoring device ofthe present invention can measure intraocular pressure with highaccuracy without the aid of a wire and has a structure in which thesensor and its important parts are sealed per se. Therefore, in additionto being accurate and safe, therefore, the device itself needs nopackages.

53. The present invention has been described in an illustrative manner,and it is to be understood the terminology used is intended to be in thenature of description rather than of limitation. Many modifications andvariations of the present invention are possible in light of the aboveteachings. Therefore, it is to be understood that within the scope ofthe appended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A device for remote monitoring the internalpressure of animal organs, said device comprising: a glass substratehaving a coefficient of thermal expansion as large as that of silicon; ametal electrode which is formed at a predetermined thickness on acentral area of the glass substrate; an inductor which is formed at apredetermined thickness on the glass substrate by a copperelectroplating process, surrounding the metal electrode at apredetermined distance; a silicon cover, consisting of a silicondiaphragm and a cover structure, which is bonded on the glass substratein such a manner that the silicon diaphragm and the cover structurecover the metal electrode and the inductor, respectively, without adirect contact between them, thereby shielding the metal electrode andthe inductor from the external environment; a contact which is formed onthe glass substrate, extending from a junction between the glasssubstrate and the silicon cover to the inductor to electrically connectthe silicon cover to the inductor.
 2. A method for fabricating asealed-type device which remotely senses the internal pressure of animalorgans, said method comprising the step of: depositing a metal electrodeon a central area of a glass substrate with a coefficient of thermalexpansion as large as that of silicon, the metal electrode playing arole as a lower electrode for a capacitive pressure sensor; forming apattern of an inductor at a predetermined thickness by copperelectroplating, said inductor surrounding the metal electrode at apredetermined distance; etching a central area of a silicon substrate toform a space for enveloping the metal electrode; forming a pattern of agroove around the space in the silicon substrate by a etching process;diffusing boron ions shallowly into the space and deeply into the grooveto form etch barriers thereat; bonding the silicon substrate on theglass substrate through an anodic bonding in such a way that the metalelectrode and the inductor are enveloped in the space and the groove,respectively; and etching the silicon substrate from its rear side tothe extent that the etch barriers are exposed.
 3. A method as set forthin claim 2 , wherein the metal depositing step comprises etching acentral area of the glass substrate, and depositing Au/Cr on the etchedarea.
 4. A method as set forth in claim 2 , wherein the inductor isformed by electroplating copper at a thickness of 30 μm and used toobtain a photoresist film in which the ratio of line to space is 15μm/15 μm.
 5. A method for fabricating a sealed-typed remotepressure-monitoring device, in which an inductor and a capacitivepressure sensor are integrated in a chip on a glass substrate with anelectrical connection therebetween, to form a pressure sensor which issealed per se, whereby no packages are needed for insertion into thebody and a low parasite capacitance and a high Q value can be obtained.